Safe disposal of by-prodcut nitgrogen trichloride (NCl.sub.3) has long been a problem in the manufacture of trichloroisocyanuric acid. NCl.sub.3 is generally present, to an extent dependent on cyanuric acid chlorination process details, in the vent gas from the reactor. Such vent gases usually include nitrogen, carbon dioxide, chlorine and water vapor. Both environmental and economic reasons dictate the recovery of chlorine from these vent gases. However, the NCl.sub.3 must first be removed to prevent accumulations of dangerous concentrations of NCl.sub.3 as a result of repeated reuse (recycling) of the recovered chlorine. Additionally, NCl.sub.3 may remain in the liquid (slurry) reactor effluent, in which case it tends to be driven off during subsequent solids drying operations.
NCl.sub.3 is usually removed from gas streams by contacting them with concentrated hydrochloric acid, which converts the NCl.sub.3 to ammonium chloride. The latter product is soluble and constitutes a disposal problem which is generally handled by base treatment to liberate ammonia and form a chloride brine.
U.S. Pat. No. 3,184,458, for example, teaches that NCl.sub.3 can be removed from recycle chlorine and inert stripping gases by scrubbing with acid. However, disposal of the used acid by sewering is taught and this is now recognized as environmentally unsuitable. The patent also teaches periodic rinsing of lines and equipment with mild reducing agents, such as sodium nitrite or sulfite, to decompose accumulated NCl.sub.3. This introduces further waste disposal problems.
Other patents representative of the prior art methods of dealing with nitrogen trichloride are U.S. Pat. No. 2,969,360; 2,770,998; 3,035,056; 3,474,096; 3,534,033; 3,568,409; 3,597,156; 3,668,204 and Belgian Patent No. 644,209.
The present applicants have found nothing in the published literature suggesting that thermal decomposition has ever been considered as a feasible or desirable method for disposal of NCl.sub.3.